The present invention relates to an improved slip for gripping tubulars in a rotary table to support the tubular from the table. In more detail, the present invention relates to a power slip that provides full retraction of the slip segments that is of minimal vertical dimension for added safety and ease of use. The present invention is particularly useful for running drill pipe into and out of a well bore and for running casing pipe into a well bore.
There are various situations in which it is necessary or desirable to temporarily support the weight of a drill or casing string with tapered slips received within a tapered slip bowl while an upper joint or stand of pipe, or other structure, is being connected to or disconnected from the string. To speed the set and release of such slips, a number of power slips are available that act to move the slip segments upwardly and downwardly (relative to a co-acting slip bowl) into and out of engagement with the tapering camming surface of the bowl, and therefore into and out of engagement with the drill pipe or casing joint. Examples of such slips include the VARCO PS-15 and PS-16 (National Oilwell Varco, Houston, Tex.) power slips as well as those available from Den-Con Tool Co. (Oklahoma City, Okla.).
Although these prior power slips are in current use and function for their intended purpose, there are a number of opportunities for improvements, particularly in connection with their ease of use. One such opportunity for improvement relates to the vertical height of the power slip, and therefore its size, weight, and ease of installation. More importantly, however, a short power slip provides advantages in safety and clearance.
These advantages of safety and clearance are provided by using pins that sit down into the holes in the pin drive master bushing to provide additional vertical stroke for the cylinders that lift the slips to the raised position up and away from the drill pipe or casing, thereby providing sufficient retraction of the slips while minimizing the vertical dimension of the power slip.
The power slip of the present invention also provides an advantage over known prior art slips (such as the Varco power slip) in that it utilizes a dual linkage and independent slip assemblies. The dual linkage provides for additional stroke length in retracting the slips by folding upwardly upon itself. Independent slip assemblies (as compared to the slip assemblies in known prior art power slips, which are linked with a hinged pin connection, and retract and set the same distance at the same time) allow the power slip of the present invention to accommodate off-center drill pipe and/or casing.
Known prior art power slips utilize gravity to cause the slips to fall back into the retracted position. The Varco PS-15 and PS-16 power slips, for instance, are provided with steps on the back of the slip segments for the purpose of facilitating the falling of the slips back from the pipe. The power slip of the present invention, however, utilizes a cable to pull the slips up and back away from the drill pipe and/or casing, thus providing a positive clearance between the tubular and the opening through the power slip, all while minimizing the vertical height of the power slip and maintaining sufficient stroke to fully retract the slip segments.
It is, therefore, an object of the present invention to provide a power slip with minimal vertical height that also provides sufficient retraction of the slips to insure that the slips are raised far enough from drill pipe or casing positioned between the slips to provide sufficient clearance when in the retracted position while providing the advantages of safety and clearance off a power slip of minimal height.
Another object of the present invention is to provide a power slip that uses a modified set of SDXL slip segments (so-called “extra long slips” as known in the art), eliminating the need for a guide ring and allowing for regular drilling bowls to be used as a back-up for the slips.
Another object of the present invention is to provide a power slip that directly engages the pin drive master bushings of the rotary table, utilizing the depth of the drive pin holes as part of the actuators, thus allowing the power slip to set at a lower height.
Another object of the present invention is to provide a power slip that fits directly over the master bushing, with no panels or other equipment extending over the rotary table, reducing the likelihood of possible injury and facilitating movement by rig personnel.
Other objects, and the many advantages of the present invention, will be made clear to those skilled in the art in the following detailed description of several preferred embodiments of the present invention and the drawings appended hereto. Those skilled in the art will recognize, however, that the embodiments of the invention described herein are only examples provided for the purpose of describing the making and using of the present invention and that they are not the only embodiments of power slips that are constructed in accordance with the teachings of the present invention.